LAT is now called ALAT (Approximate Lowest Astronomical Tide)

In the Dutch part of the North Sea, Wadden Sea and Ooster- and Westerschelde, the name of the reference plane has changed from 1 January 2026. Lowest Astronomical Tide (LAT) is now called Approximate Lowest Astronomical Tide (ALAT).

Nothing will change in navigation practice, but the Navy’s information is useful:

The standard reduction plane for nautical charts is the Approximate Lowest Astronomical Tide. This is the lowest possible water level based on the position of the sun and moon. Water levels below ALAT also occur, due to weather conditions such as high atmospheric pressure or offshore winds.
The North Sea Hydrographic Commission (NSHC) plays a coordinating role in setting reduction surfaces for the North Sea. Yet the location of ALAT on the borders of North Sea countries is slightly different everywhere. And some hydrographic services even use a different definition. Now this has been neatly equalised by international agreements. Other applications (such as off-shore and oceanography) use a different reduction plane at sea: the mean sea level or Mean Sea Level (MSL)

The annual publication HP33 shows how NAP, MSL and ALAT relate to each other at particular locations. This is needed because harbour masters and lock keepers often give the water level in NAP. The reference plane for both the lower rivers and Caribbean Netherlands has therefore not changed. These are already displayed according to ALAT.

Source: Dutch Ministry of Defence.